In general, there are two types of XY recorders in common usage. There is the stationary paper type and there is the moving paper type. In the stationary paper type, the size of the plotting surface is limited by the size of the web which the recorder can hold. In the moving paper type, the size of the plot is limited only as to the width of the web, i.e., the web may be of any desired length since one degree of freedom is being achieved by the movement of the web.
In the moving web type XY recorder, the web is moved typically by means of registration holes along each edge of the web that are parallel to the direction of travel of the web with toothed driving wheels meshing with those registration holes to impart movement to the web. The moving paper type XY recorders that do not use the registration holes along the edge typically have a defined channel that extends the full length of the plotting surface and is substantially the same width as the web. This confines the web so there is no side to side motion as the web is advanced through that channel.
To increase plotting speed, it is desirable to be able to plot in both directions, both forward and backward. Unless some provisions have been made to prevent slippage of the paper either from side to side or from end to end, the accuracy of the plot will be greatly reduced since the element of repeatability will be missing. A web having the registration holes along its edge minimizes slippage at the cost of a more complex driving system and more expensive web material. The other type of moving web recorder typically relies on the narrow, long defined channel through which the web is advanced and retracted during plotting. However, this does not cure the problem of slippage from end to end. This second type of recorder also presents a considerable amount of friction between the two edges of the web and the long channel through which it passes, thus adding drag to the web and limiting the speed at which the web may be advanced and retracted during plotting. Also, in this configuration, web width tolerances can make the web too tight or too loose in the channel resulting in side to side movement or buckling of the web, further increasing plotting inaccuracies.
In both of these types of recorders, both edges of the paper are typically driven requiring a recorder that is at least as wide as the web. Additionally, many of these recorders use a heavy and necessarily slow pen head means that rides on a bar that spans the width of the web.
It would be desirable to have an XY recorder that is smaller in size, does not require registration holes along the edge of the web to achieve repeatability, and is capable of high speed operation.